The present invention relates to image forming apparatuses. More particularly, the invention relates to an image forming apparatus used for copying originals of color images and line images such as characters.
Image forming apparatuses employing a color electrophotographic system, a silver halide color photographic system, and a photosensitive/pressure-sensitive color material system and which are used to copy color images are well know in the art.
In an image forming apparatus operating in accordance with the color electrophotographic system, in general, for the color red, for instance, a color original is exposed through a red color separation filter, an electrostatic latent image of the exposed original is formed on a photo-receptor drum which is then charged and developed with cyan color toner, and the resultant toner image is transferred onto an image receiving sheet and subjected to fixing. Then, for blue and green, the above-described operations are repeatedly carried out in the same manner, thereby to obtain a color image.
Further, in an image forming apparatus employing the silver halide color photographic system, a silver halide color photosensitive material is used for reproduction of a color image.
In an image forming apparatus operating in accordance with the photosensitive/pressure-sensitive color material system, a photosensitive pressure-sensitive color photosensitive material is used to reproduce a color image.
An example of a photosensitive/pressure-sensitive color material is disclosed in commonly assigned Unexamined Published Japanese Patent Application (OPI) No. 179836/1982. The color photosensitive material is subjected to optical exposure so that a polymerizing compound is hardened in a pattern corresponding to the image to be formed, and is then pressed to obtain a visible image. The color photosensitive material includes a support and synthetic high molecular resin-wall capsules provided on the support which contain a vinyl compound, a photopolymerization initiator and a coloring agent precursor.
A photosensitive material of a type containing silver halide is optically exposed, and then subjected to thermal developing so that the silver halide is developed, while the polymerizing compound is hardened in association with the developing operation The material is pressed to obtain a visible image. Such a system is disclosed in commonly assigned Unexamined Published Japanese Patent Application (OPI) Nos. 278849/1986 and 209444/1987. In the case of the photosensitive material disclosed in commonly assigned Unexamined Published Japanese Patent Application (OPI) No. 278849/1986, after the thermal developing operation, a color image forming material is transferred onto an image receiving material having an image receiving layer, as a result of which an image is formed on the image receiving material. The photosensitive material is formed by coating a support at least with a photosensitive silver halide, a reducing agent, a polymerizing compound, and a color image forming material. Of these materials, at least the polymerizing compound and the color image forming material are confined, in combination, in microcapsules.
In the case of the photosensitive material disclosed in commonly assigned Unexamined Published Japanese Patent Application (OPI) No. 209444/1987, no image receiving material is used, and an image is formed on the photosensitive material. The photosensitive material is formed of a light-sensitive layer on a support, with the former using a silver halide, a reducing agent, a polymerizable compound, and two kinds of material which cause a coloring reaction to take place when contacted. One of the two kinds of material that enter into a coloring reaction and the polymerizable compound are contained in combination in microcapsules, while the other material is situated outside the microcapsules.
A method of forming an image using the photosensitive material has been disclosed in the aforementioned commonly assigned Unexamined Published Japanese Patent Application (OPI) No. 278849/1986.
This image forming method proceeds as follows: First, the photosensitive material is subjected to optical exposure to form a latent image thereon. The polymerizable compound in the region of the photosensitive material where the latent image is present is polymerized by heating or with the optical energy used in the formation of the latent image, to produce a high molecular compound, thereby to harden the capsules. Then, the photosensitive material thus treated is superposed on an image receiving material having an image receiving layer onto which the color image forming material can be transferred, and is then pressurized together with the image receiving material so that some of the microcapsules in the region of the photosensitive material where no latent image is present are ruptured. As a result, the color image forming material is transferred onto the image receiving material to form an image thereon.
In the formation of a color image according to the color electrophotographic system, the steps of charging, exposing, developing, and transferring are carried out at least three time. Accordingly, the formation of a color image using the color electrophotographic system takes a relatively long time and requires a relatively intricate and bulky apparatus. Furthermore, due to the superposition of the three color toner images, mismatching may occur, and it is difficult to obtain line images in the form of sharp and clear characters or the like.
On the other hand, in the silver halide color photographic system, although optical exposure needs to be carried out only once, troublesome wet processing operations such as developing, bleaching, fixing, and washing of the photosensitive material must be carried out. It is necessary to provide tanks for holding processing solutions for these various processing operations. As a result, the apparatus is unavoidable bulky, and the required maintenance work, such as replenishing and replacing the processing solutions, is troublesome.
The above-described photosensitive/pressure-sensitive color material system has been proposed for the purpose of eliminating the difficulties accompanying the color electrophotographic system and the silver halide color photographic system and to thus obtain a color image with ease. However, neither the photosensitive/pressure-sensitive color material system nor the conventional color image forming apparatus for copying color originals containing both color images and line images such as characters can obtain line images of characters or the like which are high both in density and in sharpness, although they can achieve color images excellent in color reproduction.